combining sin and sind

[Earl A. Killian <Killian at MIT-MULTICS>]

Instead of having both sin and sind (arguments in radians and degrees)
respectively, how aobut defining sin as
          (defun sin (x &optional (y radians)) ...)
Where the second optional argument specifies the units in "cycles".
You'd use 2*pi for radians (the default), and 2*pi/360 for degrees.  To
get the simplicity of sind, you'd define the variable degrees to be
2*pi/360 and write (sin x degrees).